a. Field of the Invention
The instant invention is directed toward the use of longitudinally-mounted external coolant tanks (particularly liquid nitrogen tanks) to supply cooling to a cryogenic liquid (particularly liquid helium) transport container.
b. Background Art
Liquid helium is shipped in vacuum-insulated, double-walled intermodal tank containers that consist of one or more outer vacuum vessels, each encapsulating one or more thermally insulated cryogenic liquid inner vessels suspended by a low heat leak support system. A thermal shield cooled by liquid nitrogen is placed in the annular space between the helium-containing inner vessel and the outer vacuum vessel to reduce heat leak to the helium. The entire system, including all piping and appurtenances, must fit within a structural framework of standardized length and width.
Helium is a rare and expensive resource that is found in only a few locations in the world. It is primarily used in the United States, Japan, and Western Europe, often far from the limited supply points. Helium is shipped as an extremely cold liquid with a normal boiling point of xe2x88x92452xc2x0 F. and is exceptionally temperature sensitive. Liquid nitrogen, a less expensive product with a normal boiling point of xe2x88x92320xc2x0 F., is used to thermally shield the colder helium.
Shipping expenses are a significant portion of the delivered cost of liquid helium because of its low density and exotic shipping container. Helium containers presently use an internal liquid nitrogen coolant supply vessel located at the aft end of the container adjacent to the liquid helium vessel; both are surrounded with a single outer vacuum jacket. This location prevents the helium inner vessel from extending the full length of the standardized frame. A longer helium inner vessel would increase the payload per transit improving the transportation economics.
Liquid helium container design has focused on reducing heat leak to the helium to achieve a nonventing hold time of over 30 days. The first liquid helium containers used a transverse mounted external liquid nitrogen tank located in an elevated position across the rear end of the container. This design significantly limits the actual length of the liquid helium inner vessel. Advantages of the design included ample space for external piping and valves, gravity head aiding the liquid nitrogen transfer to the thermal shield, and simpler fabrication of the main tank assembly.
U.S. Pat. No. 3,782,128, issued Jan. 1, 1974, reflects current container design that employs a circumjacent internal liquid nitrogen vessel. The contents of this patent are hereby incorporated by reference as though fully set forth herein. The liquid helium inner vessel uses more, but still not all, of the standardized frame length and adds about 1500 gallons of capacity over the previous design. Disadvantages include a complex tank assembly and support system, limited space for external piping and valves, liquid nitrogen supply distribution dependent upon regulated pressure differential, and the liquid helium inner vessel length is still limited by the liquid nitrogen supply location. No known prior design locates the liquid nitrogen supply in a position that does not restrict the liquid helium inner vessel length.
The present invention maximizes the liquid helium volume that can be transported in the container by employing one or more liquid nitrogen coolant tanks mounted in an elevated longitudinal position running primarily parallel to the helium tank assembly. This arrangement allows the liquid helium inner vessel to extend the entire forty feet of a standard container adding an additional capacity of up to 1000 gallons over current art. The helium tank assembly and support system is simpler. The high elevation of the coolant supply tanks also ensures that the thermal shield stays liquid-filled because of gravity and also reduces the required operating pressure and corresponding saturated liquid temperature, thus further reducing heat leak to the helium.
The inventive aspects include the location, mounting, and interface of the liquid nitrogen supply tank(s). One or more long, narrow vacuum-jacketed external nitrogen tanks are efficiently located in a previously unused portion of the container envelope. The mounting provides structural support of the external nitrogen supply tanks that is isolated from the helium inner vessel support system. The elevation and piping interface provides the maximum possible static pressure head when feeding the liquid nitrogen cooled thermal shield. The liquid nitrogen vessels may also have a cross-sectional shape other than round because of the lowered operating pressure.
The present invention includes a fluid-transporting container comprising the following: a space envelope defined by a plurality of frame corner castings in which the space envelope has a length; a plurality of container end frames are connected to the frame comer castings thereby defining a support system; a cryogenic liquid storage tank adapted to contain a cryogenic liquid which extends the length of the space envelope and suspended by the support system; at least one coolant tank adapted to contain a cooling liquid, which is mounted at least partially above the storage tank and within the space envelope; at least one thermal shield surrounding at least a portion of the cryogenic liquid storage tank; and a fluid supply system operatively connecting the coolant tank(s) and the thermal shield(s).
The present invention further includes a cryogenic fluid-transporting system comprising the following: a cryogenic liquid storage tank adapted to contain liquid helium having a first outer vessel and a first inner vessel, thereby defining an annular vacuum space between said first inner and outer vessels; at least one thermal shield in the annular vacuum space to reduce heat leak from the first outer vessel to the first inner vessel; at least one elongated coolant tank having a second inner vessel adapted to contain a cooling liquid and a second outer vessel surrounding the second inner vessel thereby defining a second annular vacuum space between the second inner and second outer vessels, in which the elongated coolant tank(s) is mounted at least partially above the cryogenic liquid storage tank; and a fluid supply system operatively connecting the elongated coolant tank(s) and the thermal shield(s).
The present invention further includes a system for transporting liquid helium comprising the following: a relatively larger liquid helium tank assembly adapted to contain liquid helium in which the liquid helium tank assembly has a first longitudinal axis; at least one thermal shield extending at least partially around a portion of the liquid helium tank assembly; and at least one relatively smaller liquid nitrogen supply tank assembly adapted to contain liquid nitrogen in which each liquid nitrogen tank assembly has a second longitudinal axis, wherein each relatively smaller liquid nitrogen supply tank assembly is mounted in an elevated position relative to the relatively larger helium tank assembly, and in which each second longitudinal axis is oriented substantially parallel to the first longitudinal axis, and further wherein the liquid nitrogen tank assembly(ies) is in fluid communication with the thermal shield(s) to supply a controlled quantity of liquid nitrogen to the thermal shield(s).
The present invention further includes a cryogenic fluid-transporting system comprising the following: a space envelope defined between a plurality of opposed pairs of container end frames, wherein the space envelope has an upper portion and a lower portion; a first vacuum-insulated, double-walled intermodal tank comprising a first outer vacuum vessel mounted in the lower portion of the space envelope between the opposed pairs of container end frames, and a first inner vessel suspended within the first outer vacuum vessel by low heat leak structural supports, wherein a first annular vacuum space exists between the first inner vessel and the first outer vacuum vessel; a pair of second vacuum-insulated, double-walled intermodal tanks each comprising a second outer vacuum vessel mounted in the upper portion of the space envelope between the opposed pairs of container end frames and at least partly above the first outer vacuum vessel, and a second inner vessel suspended within the second outer vacuum vessel by low heat leak structural supports, wherein a second annular vacuum space exists between the second inner vessel and the second outer vacuum vessel; at least one thermal shield extending at least partially within the first vacuum jacket to reduce heat leak to the first inner vessel; and trace lines extending along and in thermal contact with the thermal shield(s) in which the trace lines are in fluid communication with each of the two second inner vessels.
Other aspects, features, and details of the present invention will be apparent from reading the following description and claims, and from reviewing the accompanying drawings.